1. Field of the Invention
This invention relates to optical resonators for lasers and especially to an improved, common-pass decentered annular ring resonator (CPDARR) for a laser.
2. Description of the Prior Art
The CPDARR, which is described in detail later herein, is an outstanding annular ring resonator. It possesses good: (1) transverse mode discrimination; (2) fundamental mode stability; (3) beam quality; and (4) power extraction efficiency. It is relatively insensitive to odd azimuthal periodicity perturbations on the conical mirrors and to waxicon and rear cone misalignments. The only area where a potential problem exists concerns its mechanism for producing a uniformly polarized output beam. It cannot employ conventional high-reflectance coatings on its conical mirror surfaces, but must employ specially designed phase-shift coatings. For example, a special 90-degree phase-shift coating can be applied to the rear conical mirror. With such a coating, the rear cone preserves the polarization state instead of scrambling it and the resonator output beam is uniformly polarized. But phase-shift coatings present a higher risk than conventional coatings. Compared to conventional coatings, the phase-shift coatings generally have: (1) a greater number of dielectric layers; (2) stricter layer-thickness tolerances; (3) higher absorption; and (4) potentially lower damage-threshold intensity levels.